Rachel Brock, daughter of Maricopa County Supervisor Fulton Brock, was in court this morning where she pleaded not guilty to charges that she had sex with a then-13-year-old boy when she was 18.

The boy is the same child whom her mother, Susan Brock, was convicted of sexually abusing for three years starting when the boy was 14.

In a twist, prosecutors say they have a letter written by Susan Brock claiming her daughter admitted to having oral sex with the underage victim. As a result, they say, their case against Rachel Brock is much stronger.

Brock originally was arrested on December 30, but she was released because charges against her were not filed by the Chandler Police Department within 48 hours of her arrest.

But Brock's back in the joint -- she was arrested at her home Friday afternoon and charged with five counts of sexual conduct with a minor and one of furnishing obscene materials to a minor -- all non-bondable offenses.

Brock is accused of having multiple sexual encounters with the boy -- a family friend she met through the Mormon Church -- beginning when the two were vacationing together in California.

The sexual trysts continued when they got home in places like Brock's car and the home of her county supervisor father.

Brock's also accused of sending a video of herself masturbating to the victim, which he showed to at least one his friends.